This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. Primary support for the subproject and the subproject's principal investigator may have been provided by other sources, including other NIH sources. The Total Cost listed for the subproject likely represents the estimated amount of Center infrastructure utilized by the subproject, not direct funding provided by the NCRR grant to the subproject or subproject staff. The overall goal of this proposal is to test the hypothesis that deep sequencing of the microbiome in the CF lung will provide novel information that will guide the clinical use of antibiotics to reduce the bacterial burden in CF. Here we will document and characterize the responsiveness of bacterial populations in the CF lung to Abx therapy in the lung. We propose that such data may provide critical insight into developing new therapeutic approaches for the treatment of CF lung infections. In addition, our microbiome analyses will provide baseline data for the future assessment of novel Abx, and other therapies, in CF patients. We will use state-of-the-art deep sequencing of bacterial populations to gain a complete picture of microbial populations in the lungs of individuals with CF on or off inhaled Tobramycin therapy. We will compare the total numbers (i.e., microbial burden), numbers of species (i.e., diversity) and which species are present (i.e., composition) in patients relative to their Abx treatment status. Because clinical observations have shown that Abx-mediated reductions in some populations result in increases in levels of other potential pathogens, the microbiome approach is key to determine the overall efficacy of Abx in complex CF lung infections. We propose the following Aims: Aim 1. Test the hypothesis that the burden, diversity and composition of bacteria in the CF lung change as a function of Abx treatment. Aim 2. Test the hypothesis that we can identify combined Abx therapies that are more efficacious against polymicrobial biofilms using our in vitro model of biofilm formation on airway cells.